Because IPS-LCD devices have the advantages of portability, wide viewing angle, low power consumption, and low radiation, they have been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), video cameras, and the like. Furthermore, LCD devices in general are considered by many to have the potential to completely replace CRT (cathode ray tube) monitors and televisions.
Referring to FIG. 9, a typical IPS-LCD panel 300 includes a color filter (CF) substrate 310, a thin film transistor (TFT) substrate 320 facing the CF substrate 310, and a liquid crystal layer 330 sandwiched between the two substrates 310, 320.
Referring also to FIGS. 7 and 8, the TFT substrate 320 includes a plurality of gate lines 321 that are parallel to each other and extend along a first direction, and a plurality of source bus lines 322 that are parallel to each other and extend along a second direction orthogonal to the first direction. The gate lines 321 and source bus lines 322 thereby define a plurality of pixel regions (not labeled). In each pixel region, the TFT substrate 320 further includes two overlapping pixel electrodes 325 parallel to the source bus line 322, a pair of shield metal lines 323 located at two opposite sides of the two overlapping pixel electrodes 325, and two common electrodes 326 that are parallel to the pixel electrodes 325 and partly overlap the shield metal lines 323 respectively. One of the common electrodes 326 is positioned between the two overlapping pixel electrodes 325 and the source bus line 322. The other common electrode 326 is positioned between the two overlapping pixel electrodes 325 and an adjacent source bus line 322. The source bus line 322 is made of metal.
In each pixel region, the common electrodes 326 and a top one of the pixel electrodes 325 are in a same layer on the TFT substrate 320, and can be made of transparent material such as indium-tin oxide (ITO). The other bottom pixel electrode 325 is made of metal, and is formed in a different layer from the layer having the common electrodes 326 and the top pixel electrode 325. In particular, an interlaminated insulating film 329 separates the common electrodes 326 and top pixel electrode 325 from the bottom pixel electrode 325. The two overlapping pixel electrodes 325 in different layers are connected by a through-hole 3251.
Generally, the common electrodes 326, the source bus line 322 and the dielectric insulating film 329 therebetween form a plurality of first capacitors C1. The top pixel electrode 325, an adjacent one of the common electrodes 326 and the dielectric insulating film 329 therebetween form a plurality of second capacitors C2.
Referring also to FIGS. 10 and 11, because the common electrodes 326 are made of transparent ITO and the source bus line 322 and the shield metal lines 323 are made of metal, a resistance along a given length of each of the common electrodes 326 is about five hundreds times that of the source bus line 322 or each of the shield metal lines 323 along a same given length. Thus, the resistances of the source bus line 322 and the shield metal lines 323 can effectively be ignored with respect to the resistances of the common electrodes 326.
Each of the common electrodes 326 can electrically be considered to be a plurality of resistors R1 joined in series in a column direction (as illustrated), wherein the effective resistance of each resistor R1 is a constant. Each first capacitor C1 and a corresponding second capacitor C2 are joined in series between the source bus line 322 and the top pixel electrode 325 in a row direction (as illustrated). The first capacitor C1 is connected to the source bus line 322, and the second capacitor C2 is connected to the top pixel electrode 325. A connecting node (not labeled) is defined between each first capacitor C1 and the corresponding second capacitor C2. Two ends of each resistor R1 are respectively connected to two corresponding connecting nodes. Because the source bus line 322 is used to provide image signals to the pixel electrode 325 via a switch element (not labeled), the source bus line 322 can be considered to be a signal source.
Operation of the IPS-LCD panel 300 has the following disadvantage. When an external circuit (not shown) provides image signals to the source bus line 322, the image signals may partly leak because of the capacitances of the first and second capacitors C1, C2, in which case the leaked signals may be capacitively coupled to the top pixel electrode 325 via the first and second capacitors C1, C2. Thus considerable crosstalk can occur between the source bus line 322 and the top pixel electrode 325.
It is desired to provide an IPS-LCD panel which overcomes the above-described disadvantage.